1. Field of the Invention
The present invention relates to a method of manufacturing a lens presenting a graded tint, the lens being suitable for use in making spectacles. The term “lens” is used to cover any optical element that is for fitting to spectacles or the like and regardless of whether it performs any correcting function.
2. Description of the Related Art
Lenses exist which present tint that is graded, i.e. tint of intensity that varies generally from the top edge of the lens towards the bottom edge of the lens. The intensity of the tint is strongest close to the top edge of the lens in the zone of the lens that is most usually struck directly by the sun's rays, while the intensity of the tint is weaker close to the bottom edge of the lens so as to minimize its influence on the user's vision.
It is known to make such lenses by associating a first layer of thermoplastic material that is tinted with a second layer of thermoplastic material that is not tinted, the layers having thicknesses that vary in substantially complementary manner. This makes it possible to make sunglasses, sunscreens, tinted vision-correcting spectacles having a single focus, tinted correction lenses having progressively-varying focus, and all presenting tint that is graded.